In the world of relationships, the most important numbers to learn are: five to one. That is the ratio of positive interactions to negative ones that predicts whether a marriage will last or become one of the sad statistics of divorce.

It isn't that you can't argue with your spouse. But the couples that make it also manage to deliver positive emotional messages even when they don't see eye to eye.

"When the masters of marriage are talking about something important, they may be arguing, but they are also laughing and teasing and there are signs of affection because they have made emotional connections," says psychologist John Gottman, Ph.D., who has developed a mathematical model of relationships. "But a lot of people don't know how to connect or how to build a sense of humor, and this means that a lot of fighting that couples engage in is a failure to make emotional connections. We wouldn't have known this without the mathematical model."

The Masters of Marriage is Gottman's term for the long-term happily married. Gottman has been observing couples for decades and measuring their every blip—from blood pressure to facial grimace during their interactions.

All the observations have been quantified and turned into a kind of Dow Jones Industrial average for marital conversations. Gottman has found that marriages fall into the danger zone for divorce when the ratio of positive to negative interactions falls below five to one. Just by watching a videotape of a couple in the first few moments of a conversation about an area of marital contention, Gottman can predict with 94 percent accuracy which couples will later divorce.

In describing and quantifying the positive and negative forces on relationships, Gottman has found that a heavily weighted factor is whether one partner will accept influence from the other. A crucial predictor of divorce is a man's unwillingness to be influenced by his wife's suggestions or his blindness to her emotional expressions.

Along with a team of mathematicians, Gottman has developed what he calls bilinear influence functions. These describe a person's ability to affect his or her spouse's mood, a kind of emotional contagion. Good couples routinely influence each other's moods, in a positive direction.

Some couples, are "volatile"—they often unleash anger at one another but they offset that anger with even larger doses of warm feelings. Despite the volatility, such couples tend to be stable and successful. They not only influence each other with anger but also with affection.

Another critical dimension is the attempt to turn a difficult conversation in a positive direction—what Gottman calls repair attempts. These typically include jokes, soothing comments or changing the subject when things are too hot. Some couples, on the other hand, are skilled at "damping" conversations—they add more negative fuel to the fire. They may make hurtful comments even when their partner is clearly trying to be positive.

In the mathematics of marriage, certain expressions of emotion carry a disproportionate amount of emotional weight. Expressions of contempt, Gottman has found, register at -4. Displays of disgust each count for three points in the negative column. Whining comes in at –1. On the other hand, a display of affection—a smile of sympathy, a touch—registers 4 on the plus side.

The good news is that you don't have to be a math whiz to have a happy marriage, and there's no one right answer. Every couple is free to write their own positive equation.